The Difference Between Forgings and Castings

　　Cast flanges are characterized by their ability to produce complex shapes that are difficult to achieve through other methods. Using cost-effective, specialized techniques, precision castings can be created with surfaces that exhibit ideal smoothness without the need for additional machining. Additionally, casting is a straightforward process, making it more affordable than forging flanges. However, cast flanges are prone to defects and porosity, particularly under conditions of severe corrosion or high pressure—issues that domestic technologies currently cannot fully address when it comes to ensuring the quality of forged components. So, let’s explore together the key differences between forgings and castings!

　　Forged flanges, produced by shaping bar stock using forging equipment, generally cannot be used to form particularly complex components and typically require significant machining. However, forged flanges boast a dense microstructure that makes them highly resistant to internal defects. As a result, they are widely employed in the manufacturing of high-precision parts such as valve seats, valve bodies, and valve stems.

　　Although casting technology has advanced significantly, leveraging computer-aided tools to optimize both structural design and the fluid geometry of the casting process, Grade 1 or Grade 2 castings still struggle to meet standard X-ray/MT or PT quality requirements—critical standards often demanded in industries such as nuclear power plants, thermal power plants, and the petrochemical sector. As a result, welding improvements are essential. However, even after weld repairs, it remains challenging to ensure the overall quality and reliability of cast valve components. These issues sometimes persist within the welded metal framework of the castings themselves. While test bars are typically subjected to temperature testing, the resulting analysis may still yield uncertain results. Although round test bars may demonstrate acceptable chemical and physical properties, they can internally harbor subtle yet potentially detrimental defects—defects that gradually compromise both strength and corrosion resistance without being easily detected.

　　Other defects within cast valves or flanges include distinct cracks and hot cracks, which arise from the combined effects of stress concentrations caused by uneven shrinkage during solidification, as well as the low strength of the metal at temperatures close to its melting point. Casting at too-low temperatures can lead to cold shuts, while the accumulation of sand particles and slag formed after metal dissolution may result in contamination. Additionally, substandard casting practices can give rise to other types of imperfections.

　　Improving the casting to meet X-ray quality requirements relies on grinding the defective areas, welding repairs, heat treatment, and repeated testing and inspection. Even under these conditions, fine linear cracks may still appear on the valve seat and gasket surfaces—or at the contact weld ends—necessitating re-welding and further machining.

　　The casting process creates an intricate particle structure, enhancing the metal's physical properties. In the actual application of the part, proper design can guide the particles to flow in the direction of the primary stress.

　　Forged parts must be uniform, free from porosity, excess voids, inclusions, and other defects. Parts produced using this method boast an excellent strength-to-weight ratio. These components are commonly used in aircraft structures.

　　Advantages of forgings: Forgings offer the benefits of controllable, extendable and contractible cross-sections; adjustable length with contractible dimensions, as well as adaptable cross-sections that can be altered at will. Forging processes include free forging/hand forging, hot forging/precision forging, upsetting, roll forging, and die forging. Why choose forgings? Compared to castings, forged valve bodies exhibit a more uniform structure, superior density, enhanced strength integrity, improved dimensional accuracy, and significantly reduced size tolerances. Additionally, their directional (line-of-flow) internal structure provides markedly better performance in terms of strength and stress distribution compared to cast components.

　　1) High strength

　　Hot forging promotes crystallization and grain refinement, maximizing the material’s potential strength and uniformity while minimizing variations between individual parts. Meanwhile, the particle flow moves precisely along the valve body’s contour, and these continuous streamlines help reduce fatigue and lower the incidence of common failures.

　　2) Reliability

　　One of the key advantages of forged components is their forging quality, which aligns perfectly with design requirements—and to some extent, this characteristic ranks among the most important.

　　3) Structural Integrity

　　Forging eliminates internal defects, resulting in a uniform microstructure that ensures superior performance. In areas where stress and intracrystalline corrosion are particularly severe, forged components guarantee extended service life and reliable, trouble-free operation.

　　4) Consistency

　　Closed-die forging delivers precise dimensional consistency, enabling full control over critical wall thicknesses and eliminating defects caused by core displacement during the casting process. Additionally, it ensures seamless separation of steel ingots and allows for the use of 10,000- to 30,000-ton presses without any impact forces, thereby maintaining a uniform microstructure.

　　The above is an introduction to the differences between forgings and castings. If you'd like to learn more, feel free to contact us anytime!